I have a Mechmate tabletop project in progress and encountered this problem last night. Below are the steps I took to determine that the Gecko 203V had blown fuse(s).

Problem: No power on the Gecko 203V drivers, motors not turning

Last event before no power condition. I was upgrading the power supply DC voltage wires that provide DC volts to the PDMX-133.

Cause:
Cross ( positive to negative and negative to positive)/reversed wired the power supply 50VDC output that supply's the power to the PDMX-126 and the PDMX-133 where the drivers are located

Trouble shooting:
1. Did not hear or feel the motors energize.
2. Checked the power good LED on PDMx-133 - no power/not energized
* Power Down all devices..
3. Power supply DC output wires were removed and then checked for correct polarity of the power supply DC output - Bingo!! cross or reversed -wired
4. Corrected the reversed condition: applied power-started up Mach3-loaded GCode, launched -no movement on motors.
5. Double check PDMX-126 for power good- it was OK
6. Check Steps LED on the PDMX-126 - active
7. PDMX-126: J2, J3, J4 all had activity on the LED's

A. Power everything down. Removed all DC suppl wiring to the Gecko 203v, remove 2 case screws, locate green fuse(looks like a unmarked resistor in a vertical position), *Note: Fuse looks like it is soldered, but it isn't*, take a needle nose plier and clamp on the longest leg the of fuse and gently rock fuse while applying upward pressure to remove it.

B. Check for continuity.

Take your DVM set it to continuity, touch both probes together and make sure you have continuity on DVM.

Apply 1 test probe to each leg of the fuse, listen or read your DVM for continuity..

If you have no continuity your fuse is blown and needs to be replaced.

Below is the fuse part number and a link to the trouble shooting chart for the Gecko 203v drive:

Sure wish I had seen this yesterday before I ordered a new gecko. Yup fuse is blown on the gecko.
Ordered 5 from Digikey just now. 70 cents apiece and they are only a hundred miles away. I might have them tomorrow via Fedex.